The present invention relates generally to printed circuits, and more particularly, to components used in the manufacturing of printed circuits and other articles.
In the manufacture of printed circuits, namely printed circuit boards or copper clad laminates, sheets of copper foil are typically bonded with a dielectric layer of a partially cured epoxy resin impregnated with woven glass fiber (conventionally referred to as a xe2x80x9cpre-pregxe2x80x9d) as in the case of a circuit board, or onto another layer of foil as in the case of copper clad laminates. In both processes, the copper is etched to produce conductive paths. It is extremely important to avoid contamination of the copper foil sheets as any foreign matter, such as resin dust, fiberglass fibers, hair, grease, oil or the like, may result in dots, dents, deposits or pits on the copper foil that can adversely affect the formation of the conductive paths forming the printed circuits.
Contamination of a copper foil will typically occur at the different processing steps the foil undergoes from its initial formation to its use in forming printed circuits. The initial forming of the copper foil will of course affect the quality of the copper sheet. Thereafter, it is the processing steps, particularly the manufacturing steps in preparing and bonding the copper foil sheet to a substrate or to another foil sheet, that generate substantial contamination that may affect the foil. For example, after the copper foil is produced, at some point it is usually cut into sheets. Cutting elements may create small metal slivers or shavings, or other machinery and materials used in the manufacturing process may be a source of other types of contamination, such as dust, grease or oil droplets, that may fall onto the surface of the foil and may become imbedded therein as the foil passes over rollers and other surfaces.
To protect the copper foil during subsequent handling and shipping, it is known to secure a metallic substrate to one side of the copper foil to protect same. For example, U.S. Pat. No. 5,153,050 to Johnston discloses a copper/aluminum/copper laminate wherein the shiny side of a copper foil is bonded along its peripheral edges to a clean sheet of aluminum. U.S. Pat. No. 5,674,596 to Johnston further discloses securing copper to a metallic substrate, such as a steel or stainless steel substrate.
By sealing the edges of copper and the metallic substrate with a flexible adhesive, the interior surface of the copper sheet is not exposed to airborne contaminants of the type previously described. The metallic substrate basically functions as a protector, a carrier and a separator for adjacent sheets of copper foil. Similarly, it has been known to adhere to the shiny side of the copper foil a protective polymeric film that may be removed during the assembly of the copper sheet onto a circuit board or onto another copper sheet.
The purpose of the foregoing laminate is to provide protection to the shiny side of the foil during subsequent operations. It is during the application of a bonding resin onto the matte side of the copper foil, and the subsequent application of the foil and resin onto a circuit board or another sheet of foil, where contamination of the foil may occur. In this respect, basically, every processing step in forming printed circuits or copper clad laminates has a potential for producing airborne contaminants or surface contaminants that may adhere to the surface of the copper foil and that may interfere with the conductive lines to be etched therein. Thus, the elimination of any step between the production of the copper foil and the ultimate bonding of the material to a circuit board or another copper foil would substantially reduce the likelihood of the foil being contaminated.
The present invention overcomes limitations in the prior art and provides a copper foil having a metallic substrate adhered to one side of a copper foil and a dimensionally stable, partially cured adhesive layer secured to the other side of the copper foil, which adhesive layer may be later cured when the copper foil laminate is applied to a circuit board or to another layer of copper foil as part of a copper clad laminate.
In accordance with the present invention, there is provided a laminate for use in the production of printed circuits boards and copper clad laminates. The laminate is comprised of a copper foil layer having a first side and a second side. A metallic substrate is attached to the first side of the copper foil layer by a band of adhesive extending along the periphery of the copper foil layer. An adhesive film formed of a resinous material having a first surface and a second surface is applied to the copper foil, with the first surface of the adhesive film attached to the second side of the copper foil, wherein the second surface of the adhesive film faces away from the copper foil. The first surface of the adhesive film is substantially cured, and the second surface of the adhesive film is at least partially uncured. A releasable protective layer extends along the second surface of the adhesive film to protect same.
In accordance with another aspect of the present invention, there is provided a method of forming a laminate for use in the production of printed circuit boards and copper clad laminates, the method comprising the steps of:
forming a metallic laminate by joining a surface of a copper foil to a surface of a metallic substrate by applying a band of flexible adhesive along the periphery thereof;
applying a preformed, adhesive film onto the exposed surface of the copper foil, the adhesive being formed of a substantially uncured, polymeric material having a releasable protective strip; and
curing the adhesive layer, wherein the outermost layer of the adhesive adjacent the releasable protective layer is only partially cured.
In accordance with another aspect of the present invention, there is provided a laminate for use in the production of printed circuit boards or copper clad laminates. The laminate is comprised of a metal foil layer having a first side and a second side and a metallic substrate. One side of the metallic substrate is attached to the first side of the metal foil by a band of a flexible adhesive extending along the periphery of the metal foil layer. An adhesive film formed of a polymeric material having a first surface and a second surface is provided on the metal foil with the first surface being attached to the second side of the metal foil. The first surface of the adhesive film is substantially cured, and the second surface is at least partially uncured. A releasable protective film is provided along the second surface of the adhesive substrate.
In accordance with another aspect of the present invention, there is provided a method of forming a laminate for use in the production of printed circuit boards or copper clad laminates. The method comprises the steps of forming a metallic laminate by joining a surface of a metal foil to a surface of a metallic sheet by applying a band of flexible adhesive along the periphery thereof; applying a preformed adhesive onto an exposed surface of the metal foil, the adhesive being formed of an uncured, dimensionally stable polymeric material having a releasable protective layer, the adhesive being applied to the metal foil with the polymeric material in contact with the foil; and curing the adhesive, wherein at least an outermost layer of the adhesive adjacent to the releasable protective layer is only partially cured.
In accordance with another aspect of the present invention, there is provided a laminate for use in production of printed circuit boards or copper clad laminates. The laminate is comprised of a metal foil having a first side and a second side. One side of the metallic substrate is attached to the first side of the metal foil by a material extending along the periphery of the metal foil layer. The material has adhesive properties to seal the facing interior surfaces of the metal foil and the substrate. A film formed of a resinous material is attached to the second side of the metal foil, the film having a B-stage cure and having a minimum dimensional thickness. A releasable protective film is provided along the second surface of the adhesive substrate.
In accordance with another aspect of the present invention, there is provided a method of forming a laminate for use in the production of printed circuit boards or copper clad laminates, comprising the steps of: forming a metallic laminate by joining a surface of a metal foil to a surface of a metallic sheet by applying a material having adhesive properties along the periphery thereof, applying a preformed, adhesive film onto an exposed surface of the metal foil, the adhesive film being formed of a substantially uncured, polymeric material on a releasable protective film, the adhesive film being applied to the metal foil with the polymeric material in contact with the foil; cutting the laminate into sheets; and heating the laminate in a furnace at a predetermined temperature for a predetermined period of time to cure the adhesive film to a B-stage cure.
In accordance with another aspect of the present invention, there is provided a laminate for use in production of printed circuit boards or copper clad laminates. The laminate is comprised of a metal foil layer having a first side and a second side. One side of the metallic substrate is attached to the first side of the metal foil by a band of a flexible, adhesive-like material extending along the periphery of the metal foil layer. A first resin layer of uniform thickness is provided on the metal foil, the first resin layer cured to a C-stage. A second resin layer of uniform thickness is provided on the first resin layer, the second layer cured to a B-stage.
In accordance with another aspect of the present invention, there is provided a method of forming a laminate for use in the production of printed circuit boards or copper clad laminates, comprising the steps of forming a metallic laminate by joining a surface of a metal foil to a surface of a metallic sheet by applying a band of flexible, adhesive-like material along the periphery thereof to join the metal foil to the metallic sheet; applying a preformed, dimensionally stable first resin film onto an exposed surface of the metal foil, the first resin film being formed of an uncured, first resin material; applying a preformed second resin film onto the first resin film; and heating the metallic laminate and the first and second resin layers to cause the first level to be cured to a C-stage and the second layer to be cured to a B-stage.
In accordance with another aspect of the present invention, there is provided a laminate for use in production of printed circuit boards or copper clad laminates, comprising a metal foil layer having a first side and a second side; a metallic substrate, one side of the metallic substrate being attached to the first side of the metal foil along the periphery of the metal foil layer; and an adhesive film formed of a substantially uncured, polymeric material having a first surface and a second surface, the first surface being attached to the second side of the metal foil.
In accordance with another aspect of the present invention, there is provided a method of forming a laminate for use in the production of printed circuit boards or copper clad laminates, comprising the steps of forming a metallic laminate by joining a surface of a metal foil to a surface of a metallic sheet along the periphery thereof; applying a preformed, adhesive film onto an exposed surface of the metal foil, the adhesive strip being formed of a substantially uncured, polymeric material on a releasable protective strip, the adhesive film being applied to the metal foil with the polymeric material in contact with the foil; and curing the adhesive film wherein at least an outermost layer of the adhesive strip adjacent to the releasable protective layer is only partially cured.
In accordance with another aspect of the present invention, there is provided a laminate for use in production of printed circuit boards or copper clad laminates, comprising a metal foil having a first side and a second side; a metallic substrate, one side of the metallic substrate being attached to the first side of the metal foil along the periphery of the metal foil layer to seal the facing interior surfaces of the metal foil and the substrate; a film formed of a resinous material attached to the second side of the metal foil, the film having a B-stage cure and having a minimum dimensional thickness; and a releasable protective film along the second surface of the adhesive substrate.
In accordance with a further aspect of the present invention, there is provided a method of forming a laminate for use in the production of printed circuit boards or copper clad laminates, comprising the steps of forming a metallic laminate by joining a surface of a metal foil to a surface of a metallic sheet along the edges thereof; applying a preformed, dimensionally stable adhesive film onto an exposed surface of the metal foil, the adhesive film being formed of a substantially uncured, polymeric material, the adhesive film being applied to the metal foil with the polymeric material in contact with the foil; cutting the laminate into sheets; and heating the laminate in a furnace at a predetermined temperature for a predetermined period of time to cure the adhesive film to a B-stage cure.
In accordance with another aspect of the present invention, there is provided a laminate for use in production of printed circuit boards or copper clad laminates. The laminate is comprised of a metal foil having a first side and a second side. One side of a metallic substrate is attached to the first side of the metal foil to seal the facing interior surfaces of the metal foil and the substrate. A layer formed of a resinous material is attached to the second side of the metal foil. The layer has a first surface and a second surface, the first surface of the layer being attached to the second side of the metal foil and being substantially cured, and the second surface of the layer being at least partially uncured.
It is an object of the present invention to provide a metal foil laminate for use in the manufacturing of printed circuit boards and copper clad laminates.
Another object of the present invention is to provide a metal foil laminate as described above that has a metallic protective layer to protect one side of the metal foil from contamination.
Another object of the present invention is to provide a metal foil laminate as described above that has a dimensionally stable, partially uncured resin layer on one side of the metal foil.
A still further object of the present invention is to provide a metal foil laminate as described above, wherein a portion of the resin layer in contact with the metal foil is fully cured, and a portion of the resin layer facing away from the metal foil is only partially cured.
A still further object of the present invention is to provide a metal foil laminate as described above having a removable protective layer on the partially cured portion of the resin layer.
A still further object of the present invention is to provide a metal foil laminate as described above, wherein the resin layer in contact with the metal foil is fully cured.
A still further object of the present invention is to provide a metal foil laminate as described above, wherein the metal foil is copper and the metallic protective layer is aluminum.
A still further object of the present invention is to provide a process for curing a resin layer on a metal foil, wherein the innermost portion of the resin layer in contact with the metal foil is fully cured, and the outermost portion of the resin layer facing away from the metal foil is only partially cured.
These and other objects and advantages will become apparent from the following description of preferred embodiments of the invention taken together with the accompanying drawings.